/* 图片延迟加载
使用方法 如: $(".switch_textarea").lazyload(); 

详细出处参考：http://www.jb51.net/article/25706.htm
* Lazy Load - jQuery plugin for lazy loading images 
* 
* Copyright (c) 2007-2009 Mika Tuupola 
* 
* Licensed under the MIT license: 
* http://www.opensource.org/licenses/mit-license.php 
* 
* Project home: 
* http://www.appelsiini.net/projects/lazyload 
* 
* Version: 1.5.0 
* 
* Modify by @cnbaiying 
* Modify time: 2010-12-16 
*/ 
(function($) { 
$.fn.lazyload = function(options) { 
var settings = { 
threshold : 0, //阀值 
failurelimit : 0, 
event : "scroll", 
effect : "show", 
container : window 
}; 
if(options) { 
$.extend(settings, options); 
} 
/* Fire one scroll event per scroll. Not one scroll event per image. */ 
var elements = this; 
if ("scroll" == settings.event) { 
$(settings.container).bind("scroll", function(event) { 
var counter = 0; 
elements.each(function() { 
if ($.abovethetop($(this).parent(), settings) || $.leftofbegin($(this).parent(), settings)) { 
/* Nothing. */ 
} else if (!$.belowthefold($(this).parent(), settings) && !$.rightoffold($(this).parent(), settings)) { 
$(this).trigger("appear"); 
} else { 
if (counter++ > settings.failurelimit) { 
return false; 
} 
} 
}); 
/* Remove image from array so it is not looped next time. */ 
var temp = $.grep(elements, function(element) { 
return !element.loaded; 
}); 
elements = $(temp); 
}); 
} 
this.each(function() { 
var self = this; 
/* When appear is triggered load original image. */ 
$(self).one("appear", function() { 
if (!this.loaded) { 
//alert($(self).parent().html($(self).html())); 
var tmp_str = $(self).html(); 
tmp_str = tmp_str.replace("<", "<"); 
tmp_str = tmp_str.replace(">", ">"); 
$(self).parent().append(tmp_str); 
self.loaded = true; 
} 
}); 
/* When wanted event is triggered load original image */ 
/* by triggering appear. */ 
if ("scroll" != settings.event) { 
$(self).bind(settings.event, function(event) { 
if (!self.loaded) { 
$(self).trigger("appear"); 
} 
}); 
} 
}); 
/* Force initial check if images should appear. */ 
$(settings.container).trigger(settings.event); 
return this; 
}; 
/* Convenience methods in jQuery namespace. */ 
/* Use as $.belowthefold(element, {threshold : 100, container : window}) */ 
$.belowthefold = function(element, settings) { 
if (settings.container === undefined || settings.container === window) { 
var fold = $(window).height() + $(window).scrollTop(); 
} else { 
var fold = $(settings.container).offset().top + $(settings.container).height(); 
} 
return fold <= $(element).offset().top - settings.threshold; 
}; 
$.rightoffold = function(element, settings) { 
if (settings.container === undefined || settings.container === window) { 
var fold = $(window).width() + $(window).scrollLeft(); 
} else { 
var fold = $(settings.container).offset().left + $(settings.container).width(); 
} 
return fold <= $(element).offset().left - settings.threshold; 
}; 
$.abovethetop = function(element, settings) { 
if (settings.container === undefined || settings.container === window) { 
var fold = $(window).scrollTop(); 
} else { 
var fold = $(settings.container).offset().top; 
} 
return fold >= $(element).offset().top + settings.threshold + $(element).height(); 
}; 
$.leftofbegin = function(element, settings) { 
if (settings.container === undefined || settings.container === window) { 
var fold = $(window).scrollLeft(); 
} else { 
var fold = $(settings.container).offset().left; 
} 
return fold >= $(element).offset().left + settings.threshold + $(element).width(); 
}; 
/* Custom selectors for your convenience. */ 
/* Use as $("img:below-the-fold").something() */ 
$.extend($.expr[':'], { 
"below-the-fold" : "$.belowthefold(a, {threshold : 0, container: window})", 
"above-the-fold" : "!$.belowthefold(a, {threshold : 0, container: window})", 
"right-of-fold" : "$.rightoffold(a, {threshold : 0, container: window})", 
"left-of-fold" : "!$.rightoffold(a, {threshold : 0, container: window})" 
}); 
})(jQuery); 
